the best idea is just to play 2-3 games and review yourself what the behaviour of the emeny commanders are, that way you could easily find them and just eliminate them. This is just a tactic you can use for many of the campaign levels so just keep that in mind.
I fully agree with wakanarai, it's the best advice for this level and for many others.
After failing my first attempt(I tried to expand everywhere, it didn't end well), I looked over the history and checked where the enemy commanders hid. Then instead of focusing on expansion, I tracked them down one by one with the cards and this is how I won on my second attempt.
You don't necessarily have to play this level like some others, where you need to take every territory on the map to win. Just find the commanders and kill them. When I reached the last commander, I believe the AI had 10 or 20 times my income. But it didn't matter, since I just needed to kill the commander to end the game.